Studies on the annealing and antibacterial properties of the silver-embedded aluminum/silica nanospheres

N A N O C O M M E N T A R Y

Open Access

Studies on the annealing and antibacterial

properties of the silver-embedded aluminum/silica

nanospheres

Ko-Ying Pan

, Chia-Hung Chien

, Ying-Chih Pu

, Chia-Ming Liu

, Yung-Jung Hsu

, Jien-Wei Yeh

and Han C Shih

Abstract

Substantial silver-embedded aluminum/silica nanospheres with uniform diameter and morphology were successfully synthesized by sol-gel technique. After various annealing temperatures, the surface mechanisms of each sample were analyzed using scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. The chemical durability examinations and antibacterial tests of each sample were also carried out for the confirmation of its practical usage. Based on the result of the above analyses, the silver-embedded aluminum/ silica nanospheres are eligible for fabricating antibacterial utensils.

Keywords: Silver-embedded aluminum/silica nanospheres; Sol-gel technique; Annealing; Chemical durability examination; Antibacterial test

Background

During the last decades, owing to the greenhouse effect, the climatic anomaly has happened around our planet. The change in temperature is dramatic all over the world, the disease-causing germs threat humankind seriously, and consequently, various antibacterial materials, such as zeolite-based [1,2] and phosphate-based [3,4] composi-tions, ZnO nanoparticles [5,6], TiO2nanoparticles [7-9],

Ag nanoparticles [10-13], and core-shell silica-metal nano-compositions [14-16] are developed by researchers. Gen-erally, the core-shell silica-silver nanocomposition is the most promising item among antibacterial materials due to its unique physical and chemical properties [17,18]. Nano-silver owns a large specific surface area and a high fraction of surface atoms; silica nanospheres, a typical dielectric core material for immobilized nanoparticles, has a good chemical and thermal stability, chemical inertness, large surface area, and outstanding compatibilities with several kinds of metal nanoshells. Moreover, sundry publication studies on core-shell silica-silver nanostructures focused on various manufacturing, optoelectronics, and catalytic

and antibacterial features. It is common knowledge that the size, shape, and density of metal nanoshells and the combination of shells and cores mainly affect the presenta-tions of the core-shell silica-silver nanocomposition, so many research groups have devoted their energies to dis-covering diverse ways for a very efficient sample. Therefore, throughout the previous literatures referring to the synthe-ses of the core-shell silica-silver nanocompositions, two ap-proaches are majorly adopted: seed-mediated method and layer-by-layer (LbL) self-assembly technique [19,20].

The seed-mediated method [19], similar with electroless plating [21], includes two steps. In the first step, the sur-faces of core materials are activated by chemicals or metals; in the second step, handling the redox reaction leads Ag+ ions into metallic Ag, which coats the SiO2nanocores with

tiny Ag nanoshells. In order to obtain the accurate thick-ness of shells, these two steps must be carried out again for several times, which means that this method is a great con-sumption and its products as impurities. The idea of LbL self-assembly technique is based on the alternate deposi-tions derived from the electrostatic interacdeposi-tions between the charged components for multilayer growth on colloid particles. According the earlier published papers [22,23], LbL self-assembly technique is smart but time-consuming and unsuitable for production line. No doubt dealing with

* Correspondence:[email protected]

1

Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan

4

Department of Chemical and Materials Engineering, Institute of Nanomaterials, Chinese Culture University, Taipei 11114, Taiwan Full list of author information is available at the end of the article

© 2014 Pan et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

for calcination or sintering. However, there are few litera-tures putting emphasis on the annealing-induced proper-ties of the silver-embedded aluminum/silica nanospheres, especially at high working temperatures above 600°C. Herein, authors did the annealing separately at 250°C, 400°C, 600°C, 800°C, and 1,000°C and investigate the annealing-induced properties of the silver-embedded aluminum/silica nanospheres via material and UV-visible (UV-vis) analyses. To follow the capabilities of these pro-ducts realistically, the chemical durability test and antibac-terial examination were handled as well.

Methods

Reagent

Five reagents are used in this task as follows: tetraethyl orthosilicate (TEOS, 98%, Alfa Aesar, Ward Hill, MA, USA), absolute ethanol (99.99%, Sigma-Aldrich Corporation, St. Louis, MO, USA), silver nitrate (99.9%, Mallinckrodt Pharmaceuticals, Dublin, Ireland), aqueous

by sol-gel technique. Figure 1 is the schematic diagram of whole process flow used for silver-embedded aluminum/ silica nanospheres, which includes the annealing process. In advance, two kinds of solutions, solutions A and B, had to be prepared. Solution A was prepared by mixing 4.2 g TEOS with 17.42 g ethanol by stirring for 10 min at 35°C. As to solution B, the mixture of 0.23 g aluminum nitrate enneahydrate, 0.1 g silver nitrate, and 4.38 g DI water was combined by stirring for 10 min at 35°C. Meanwhile, add-ing 0.5 ml of aqueous ammonia drop by drop into the solu-tion B keeps the pH at approximately 6.5. Next, solusolu-tions A and B were mixed in a glass by stirring for 40 min at 35°C. Then, adding 100 ml aqueous ammonia into this com-bination maintains the pH at approximately 12.7 by stir-ring for 17.5 h at 35°C, thus saving the catalyze reaction time. While the above reaction was done, silver-embedded aluminum/silica nanospheres were collected by centrifu-gation. Eventually, the products were washed twice by ethanol and then dried in an oven at 50°C for 24 h.

After obtaining as-prepared powders, silver-embedded aluminum/silica nanospheres, the annealing processes were performed in the furnace. The as-prepared pow-ders in an aluminum boat were placed in the heating area of the quartz tube, and the pressure inside the quartz tube was kept up at 5 × 10−2 Torr by a rotary pump. The working conditions of this process were as follows: (1) The temperature was raised separately to five working parameters (250°C, 400°C, 600°C, 800°C, and 1,000°C) with the heating rate of 1.7°C/min. (2) The temperature was maintained separately at five working parameters (250°C, 400°C, 600°C, 800°C, and 1,000°C) for 1 h. (3) Each sample was cooled separately to room temperature. In the above steps, (1), (2), and (3), O2 gas was continuously injected into the quartz

tube at a constant flow rate of 4 sccm. The five anneal-ing temperatures in this experiment were 250°C, 400°C, 600°C, 800°C, and 1,000°C, and these five samples ob-tained were termed as SAS-250, SAS-400, SAS-600, SAS-800, and SAS-1000, respectively.

Characterizations of silver-embedded aluminum/silica nanospheres

Material analysis

The morphologies of each sample were characterized by scanning electron microscope (SEM, JSM-6500 F; JEOL Ltd., Tokyo, Japan) and high-resolution trans-mission electron microscope (HRTEM, JEM-2010). X-ray photoelectron spectroscopy (XPS) spectra were analyzed at an angle of 0° using PerkinElmer model PHI 1600 system (PerkinElmer Inc., Waltham, MA, USA) with Mg Kα line as an X-ray source and the en-ergy resolution was 1.6 eV; all the deconvolutions of XPS curves were performed with the XPS Peak Fitting Program (XPSPEAK41, Chemistry, CUHK; Informer Technologies Inc., Copthall Roseau Valley, Dominica). UV-visible absorption spectra were recorded using a Hitachi U-3010 spectrophotometer (Hitachi Technologies, Shanghai, China).

Chemical durability test of silver-embedded aluminum/silica nanospheres in water

In this test, the focus was on the products after annealing at high temperature, so SAS-250 was ignored. First, each of the five samples of 0.25 g powder was dispersed in 10 ml water, and the Si, Al, and Ag ions released were de-termined after 2, 4, 6, 8, and 10 days of immersion. Sec-ond, 2 ml HNO3(0.5 mM) was added into the retrieved

solution. The concentrations of Si, Al, and Ag ions re-leased from the sample into the water were measured using inductively couple plasma atomic emission spectros-copy (ICP-AES, ICAP 9000; Thermo Jarrell-Ash, Franklin, MA, USA) with a detectable limitation of 1 ppb.

Antibacterial examination of silver-embedded aluminum/silica nanospheres

Owing to the tracing of the antibacterial activity of prod-ucts accepting annealing at a high temperature, SAS-250 was neglected in the above test. This antibacterial examin-ation was based on Japanese Industrial Standards (JIS) Z 2801 method designed to test the antimicrobial activity or efficacy of plastics. Two bacterial types, Escherichia coli (E. coli) 8739 and Staphylococcus aureus (S. aureus) 6538P, were used for the antibacterial assays; E. coli and S. aureus belong to Gram-negative and Gram-positive bacteria, re-spectively. Thus, our products were verified as available for practical application in various antibacterial activities by this examination. As to the sample preparations of this test, first, a bulk using rolling depression was made by mixing 0.01 g sample powders and 0.99 g polyethylene (PE) pow-ders at 180°C for 5 min. Next, transforming the bulk to plenty of crushed grains was done by a cutting machine. Then, forming the moderately crushed grains into an anti-bacterial film was carried out by depression machine at 180°C, and the average thickness of each film was less than 0.05 mm. To investigate the comparisons objectively, the placebo film was made of 100% PE as well.

The inoculum was dispersed and diluted with 1/500 NB as appropriate so that the amount of bacteria of the test in-oculum was in the range of 2.5 × 105to 10 × 105cells/ml. After each test, the film was placed in a sterilized petri dish, using a pipette, and we took exactly 0.4 ml of the test in-oculum and then instilled it onto each test film. Next, in order to incubate bacteria, the authors set the temperature of the petri dish containing the test film inculcated with the test inoculum at 35°C and a relative humidity of not less than 90% for 24 h. After incubation, the number of colonies was counted in a serially diluted petri dish. The results of this antibacterial examination will be discussed in ‘Antibac-terial analysis of silver-embedded on aluminum/silica nano-spheres’ section.

Results and discussion

Morphologies of silver-embedded aluminum/silica nanospheres

Figure 2 shows the SEM image of abundant silver-embedded aluminum/silica nanospheres, the as-prepared sample by sol-gel method, with diameter of 500 nm [24]; these nanospheres are roughly equal in size. To observe the exact surfaces of each sample's single particle, the TEM images of each sample were taken in Figure 3. The reaction mechanisms of this sol-gel process can be explained as follows [25]. From ‘Synthesis of silver-embedded on aluminum/silica nanospheres and annealing conditions’ section and in Figure 1, two reactions in solu-tion B are triggered by adding moderate ammonia solusolu-tion. The first reaction includes two chemical processes,

chemical equations 1 and 2, which are considered as follows:

AgNO₃þ NH3⋅H2O→AgOH↓ þ NH4N O3 ð1Þ

Al3þþ 3NH3⋅H2O→Al OHð Þ3↓ þ 3NH4þ ð2Þ

Al ions and Ag ions are released by the hydrolysis of sil-ver nitrate and aluminum nitrate enneahydrate in solution B. After adding moderate ammonia drops, the combin-ation of hydroxyl ions and a lot of ccombin-ations is reacted in so-lution B, thus producing AgOH and Al(OH)3.

The second reaction is the steps after chemical equation 1, which includes chemical equations 3 and 4.

2AgOH→Ag2O↓ þ H2O ð3Þ

Ag₂O↓ þ H2Oþ 4NH3⋅H2O→2 Ag NHð 3Þ2

 

OHþ 4H2O

ð4Þ

After getting AgOH, due to unstable state itself, AgOH becomes Ag2O spontaneously, as written in Equation 3.

Meanwhile, as described in Equation 4, the ammonia still further reacts with Ag2O, hence, silver ammonia complex

ions [Ag(NH3)2] dissolve in the solution B, which is the

main source for Ag particles and Ag ions deposited on the surfaces of aluminum/silica nanospheres.

To compare the detailed morphologies of each sample, Figure 3 was enlarged in Figure 4. From Figures 3a and 4a, the silver particles of the as-prepared sample are evenly distributed around the surface and the average size is about 2.87 nm. The silver particles of SAS-250 become large as well as rough, and the average size is about 6.56 nm, as shown in Figure 4b. Few silver clusters

whose diameter is about 20 nm are also observed around the surface of SAS-250 in Figures 3b and 4b. The silver particle size of SAS-400 is smaller than that of SAS-250 and approximates to 5 nm; these silver particles are equally distributed around the surface, as shown in Figures 3c and 4c. The distribution of silver particles on 600 is almost the same as it of SAS-400, and the dimension of silver particles of SAS-600 approximates 4 nm, smaller than it of SAS-400, as shown in Figures 3d and 4d. Judging from Figure 4e,d, it is clear that the amount of silver particles of SAS-800 is less than it of SAS-600. The silver particles of SAS-1000 disappeared around the surface, and the surface becomes very smooth, as shown in Figures 3f and 4f.

In terms of SAS-250, as shown in Figures 3b and 4b, the silver particles cluster becomes large, which can be accounted for as follows. Referring with the previous paper [26], after annealing from 200°C to 700°C, the oxygen atoms consist of two sorts, Si-OH (non-bridg-ing oxygen) and Si-O-Si (bridg(non-bridg-ing oxygen), in silver nanocrystals-doped silica films. The non-bridging oxygen acts as a key factor to undergo the cation exchanging process, as depicted in reaction (5):

Si−OH þ Agþ_{→Si−O−Ag þ H}þ _ð5Þ

Therefore, due to this redox, the silver particles are de-posited on the silica surface. Additionally, De et al. [26] indicate that the Ag characteristic peaks were exhibited in X-ray diffraction (XRD) pattern, since the sample ac-cepted the annealing at and above 200°C. As for the sample which accepted the annealing under 200°C, the XRD pattern without Ag signal was also verified.

XPS analysis of silver-embedded aluminum/silica nanospheres

All binding energies were referenced to the C (1s) at 284.5 eV from carbon, and the spectrum deconvolutions were carried out with the XPS Peak Fitting Program. Figure 5a reveals the XPS survey scan of each sample. Figure 5b shows that the binding energies of Si (2p3/2)

are 102.7 eV for SAS-400 and SAS-600, and 102.9 eV for as-prepared sample, SAS-800, and SAS-1,000. Figure 5c shows that the binding energies of O (1s) are 532.3 eV for the as-prepared sample and 531.9 eV for the other samples. Figure 5d shows that all samples' binding energy of Al (2p3/2) is 74.4 eV. Indeed, the matrix of all kinds of

silver-embedded aluminum/silica nanospheres is stable

silica nanospheres, which refers to the earlier paper [27]. Figure 6 shows that the binding energies of Ag (3d5/2)

and Ag (3d3/2) are 368.1 eV and 374.4 eV, respectively.

After deconvolutions of each sample's Ag (3d5/2) curves

and integration of the areas under separated curves, the ratios of Ag0 to Ag+ can be obtained in Table 1. Ag0and Ag+ represent the silver atomic state and sil-ver ionic state, respectively. The ratios of Ag0to Ag+ from as-prepared sample to ASA-1000 have de-creased dramatically, which corresponds closely with the TEM images. These phenomena will be discussed as follows and cooperated in Figure 7. From the left part in Figure 7, in the as-prepared sample, the

binding energy of Al-O (511 KJ/mol) is higher than that of Si-O (452 KJ/mol), so one aluminum atom substitutes for one silica atom to constitute a tetra-hedral [AlO4]− in silica cells. Because of the

inter-action between the [AlO4]− structure and Ag+ ions,

the Ag+ ions and the Ag particles exist in the surface of aluminum/silica nanospheres. When the annealing is handled at 250°C, the Ag+ ion percentage goes up due to the increased Ag+ ions from the inside of Ag-embedded aluminum/silica nanospheres induced by thermal energy. From Table 1 and the middle of Fig-ure 7, in the annealing temperatFig-ure ranging from 400°C to 800°C, the Ag+ ion percentages of SAS-400,

Figure 6 XP spectra of Ag 3d3/2and 3d5/2in silver-embedded silica nanospheres. (a) As-prepared, (b) SAS-250, (c) SAS-400, (d) SAS-600, (e)

SAS-800, and (f) SAS-1000.

Table 1 XPS results of Ag0_{and Ag}+

by deconvolution of Ag (3d5/2) curve

Percentage of Ag0 _{Percentage of Ag}+ _{Ratio (Ag}0_/Ag+₎

As-prepared 92.4 7.6 12.16 SAS-250 89.6 10.4 8.62 SAS-400 75.3 24.7 3.05 SAS-600 48.2 51.8 0.93 SAS-800 31.3 68.7 0.46 SAS-1000 14.1 85.9 0.16

SAS-600, and SAS-800 increased dramatically, which is being explained via two mechanisms as follows: (1) The Ag+ ions derive from inside to the surface in the Ag-embedded aluminum/silica nanospheres under an annealing at 400°C to 800°C. The thermal energy is not enough to provide these Ag+ ions on the surface for reductions of Ag atoms, thus increasing the percentage of Ag+ ions on the surface. (2) When an-nealing temperature is at 400°C to 800°C, the species of oxygen molecules become active, easily catching free electrons from Ag particles, and then the combi-nations of [AlO4]− structures and Ag+ ions occur on

the surfaces, thus raising the percentage of Ag+ ions. From Table 1 and the right of Figure 7, the percent-age of Ag+ ions is the highest of all samples, when annealing is done at 1,000°C. Referring with the previous literature [28], in this range (annealing temperature above 800°C), the melting and liquefying during the annealing process of Ag particles on the surface is the root cause, hence the percentage of Ag atoms is much lower than the other samples, thus soaring the percentage of Ag+ions on the surface.

In terms of silver oxides, no doubt they are easily decomposed under elevated temperature. However, there are no silver oxides in each sample of our experiments. The root cause is that the nanosized Ag would be pro-duced during annealing and further vaporized at higher temperature with constant air flow.

UV-visible spectrum analysis of silver-embedded aluminum/silica nanospheres

The UV-visible absorption spectra of the seven kinds of silver-embedded aluminum/silica nanospheres are il-lustrated in Figure 8, which are consistent with the surface morphologies of each sample. In principle, these UV-vis spectra appear in the interaction between absorption sig-nals from silver nanoparticles and scattering signal sigsig-nals from silica nanospheres [29]. When the size of silver nanoparticles is less than 5 nm, the surface plasmon res-onance (SPR) absorption peak is not obviously shown at 420 nm in the wavelength scale [17,29]. The UV-visible spectra of as-prepared sample and SAS-800 show the same curve (red curve) due to their similar morphologies on their own surfaces. Owing to the densest and largest

Figure 7 Mechanisms of silver-embedded aluminum/silica nanospheres at different annealing temperatures.

Figure 9 Al, Si, and Ag ions released rates of silver-embedded silica nanospheres in water. (a) Al ions released rate of silver-embedded silica nanospheres in water. (b) Si ions released rate of silver-embedded silica nanospheres in water. (c) Ag ions released rate of silver-embedded silica nanospheres in water.

silver nanoparticles on the surface among all samples, the UV-visible spectrum of SAS-250 (purple curve) reveals the noticeable peak centered around 420 nm. Because the dimensions of silver particles are ranging from 3 to 5 nm and the scattering effects are derived from aluminum/sil-ica matrixes, UV-visible spectra of SAS-400 (blue curve) and SAS-600 (sky blue curve) disclose the close resem-blance tendency that their absorption peaks become broader and lower by comparing with the result of SAS-250. As to the UV-visible spectrum of SAS-1000 (deep green curve), due to the sample's surface without any nanoparticles, its signal is only derived from the scat-tering caused by aluminum/silica nanospheres, which looks like a line. By the way, the authors took SAS-1000 for further annealing at 600°C for 1 h under the atmos-phere of 90% N2+ 10% H2 in the quartz tube, and this

sample is termed SAS-1000-A6. The pink line is the

UV-vis spectrum of SAS-1000-A6, and the red shift is found at the wavelength of 440 nm by comparing with the spectrum of SAS-250 (purple line).

Chemical durability analysis of silver-embedded aluminum/silica nanospheres

Each sample's Al, Si, and Ag ions release tests in the water are determined, as sketched in Figure 9. The con-centrations of the three types of ions in the water (Y axis) versus examination time (X axis) are recorded for each sample. From Figure 9a, the release of Al ions of each sample starts on the 4th day and the concentrations in the water are about 0.2 ppm on the 10th day, which denotes that chemical durability of Ag ions in each sample accords with the demands in practice. Because the silica content is the largest amount of all elements in each sample, its con-tact with water is more serious than Al and Ag elements.

Figure 10 Antibacterial examinations. (a) Placebo film (100% PE). (b) Film of as-prepared sample. (c) Film of SAS-400. (d) Film of SAS-600, (e) Film of SAS-800. (f) Film of SAS-1000.

Table 2 Results of the antibacterial examinations

Test items Test results

Test methods

Place-PE As-prepared SAS-400 SAS-600 SAS-800 SAS-1000

Staphylococcus aureus ATCC 6538P

B 2.8 × 105 2.8 × 105 2.8 × 105 2.8 × 105 2.8 × 105 2.8 × 105

JIS Z2801:2000/AMDI:2006

C - <10 <10 <10 <10 2.9 × 104

R - 4.4 4.4 4.4 4.4 1

Escherichia coli ATCC 8739

B 9.3 × 106 9.3 × 106 9.3 × 106 9.3 × 106 9.3 × 106 9.3 × 106 Inoculation time 24 h

C - <10 <10 <10 <10 7.2 × 106

Therefore, the release of Si ions has begun since the test was starting, as shown in Figure 9b. Theoretically, the re-lease of Ag ions in the water must be lower than 5 ppm, which being used in the practical. In other words, the samples in this research could be useful in reality. From Figure 9c, the release concentration of Ag ions of SAS-400 on the 10th is 3.2 ppm, which is the highest degree among all samples; the release concentration of Ag ions of SAS-1000 on the 10th day is 0.26 ppm, which is the lowest number among all samples and is in keeping with the morphologies on the surfaces of samples. On the surfaces of dense Ag particles, the amounts of Si-O-Ag bonds with polarity are larger than that of Ag-Ag bonds without polarity. Therefore, in water, the interaction between Si-O-Ag bonds and water is stronger than that between Ag-Ag bonds. Consequently, Ag ions from Si-O-Ag bonds release into water are easier than that from Ag-Ag bonds.

Antibacterial analysis of silver-embedded aluminum/silica nanospheres

The petri dishes where the E. coli and S. aureus were cultivated on were contacted with each antibacterial film and placebo film, as shown in Figure 10. After a 24-h in-oculation, the antibacterial activity is

R¼ logB− logC ð6Þ

where B is the amount of bacteria after a 24-h inocula-tion of the placebo film, and C is the amount of bacteria after a 24-h inoculation of the antibacterial film. According to JIS R 1702 [30], if antibacterial activity (R) is greater than 2, it indicates that the sample has antibacterial effects. The results of antibacterial examinations are listed in Table2. It is self-evident that all samples are qualified but SAS-1000, which infers the surfaces of SAS-1000 without Ag ions adsorbed.

Conclusions

In summary, sol-gel technique has been successfully expanded to synthesize the silver-embedded aluminum/ silica nanospheres, and the diameter of the nano-spheres is about 500 nm. The ratios of Ag+ ions to Ag atoms on the surface of each sample deeply affect the optical and chemical features and are proportional to the annealing temperatures. Judging by the chemical dur-ability and antibacterial determinations for antibacterial usages in practice, all samples are eligible but SAS-1000, which indicates that silver-embedded aluminum/silica nanospheres would be the promising candidate for manu-facturing antibacterial utensils.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

KYP wrote the whole manuscript and carried out some experiments and the data analysis. CHC and YCP performed some experiments and data analysis. CML carried out the antibacterial examinations. YJH, JWY, and HCS provided the ideas, information, and facilities of this task. Mostly, HCS organized the final version of this paper. All authors read and approved the final manuscript.

Authors’ information

KYP is a PhD student at the National Tsing Hua University in Taiwan, R.O.C. and have devoted much attention to the research of nanomaterials. CHC got a master's degree from the National Tsing Hua University and now is an engineer in TSMC. YCP got a PhD degree from National Chiao Tung University and is currently a postdoctoral fellow at UC Santa Cruz in USA. CML is currently a senior supervisor in the Nano Technology Research Center. YJH is currently a vice professor at National Chiao Tung University. JWY is currently a professor at National Tsing Hua University. HCS is currently a professor at National Tsing Hua University and Chinese Culture University. Acknowledgements

This task was sponsored by the National Science Council of the Republic of China (Taiwan) under grants NSC-102-2221-E-034-003.

Author details

1_{Department of Materials Science and Engineering, National Tsing Hua}

University, Hsinchu 30013, Taiwan.2Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan.3_Nano

Technology Research Center, Industrial Technology Research Institute, Hsinchu 31040, Taiwan.4_{Department of Chemical and Materials Engineering,}

Institute of Nanomaterials, Chinese Culture University, Taipei 11114, Taiwan.

Received: 13 May 2014 Accepted: 9 June 2014 Published: 17 June 2014

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doi:10.1186/1556-276X-9-307

Cite this article as: Pan et al.: Studies on the annealing and antibacterial properties of the silver-embedded aluminum/silica nanospheres. Nanoscale Research Letters 2014 9:307.

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